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Shenyan Huang Ke An Yan Gao Akane Suzuki 《Metallurgical and Materials Transactions A》2018,49(3):740-751
Constrained γ/γ′ lattice misfit as a function of temperature (room temperature, 871 °C, 982 °C, 1093 °C, and 1204 °C) is measured by neutron diffraction on the first-generation Ni-based single-crystal superalloy René N4 and second-generation superalloys René N5, CMSX4, and PWA1484. All the alloys studied show negative misfit at temperatures above 871 °C. For René N4, René N5, and PWA1484, the misfit becomes less negative at temperatures above 1093 °C, possibly due to either the chemistry effect or internal stress relaxation. The magnitude of the misfit shows a qualitative agreement with Caron’s misfit model based on Vegard’s coefficients. The Re-free alloy René N4 was found to have a larger γ lattice parameter and γ/γ′ misfit due to higher fractions of Cr, Ti, and Mo. After 100 hours of annealing at high temperatures, René N5 shows a more negative misfit than the misfit after the standard heat treatment. 相似文献
3.
Formation of <Emphasis Type="Italic">β</Emphasis>-NiAl Phase During Casting of a Ni-Based Superalloy
A high-refractory Ni-based superalloy prototype was melted on a research scale while simulating industry practices. Ingots were vacuum induction melted and subjected to a computationally optimized homogenization heat treatment prior to fabrication which consisted of forging and hot rolling. Failure of one of the ingots at the early stage of the forging process was attributed to the precipitation of the β-NiAl phase during melting which stabilized the eutectic constituent. 相似文献
4.
Guowei Chang Shuying Chen Xudong Yue Qingchun Li 《Metallurgical and Materials Transactions A》2017,48(4):1551-1561
The morphological changes of the δ-ferrite/γ interphase boundary have been observed in situ with a high-temperature confocal scanning laser microscope (HTCSLM) during δ/γ transformations (δ → γ and γ → δ) of Fe-0.06 wt pct C-0.6 wt pct Mn alloy, and a kinetic equation of morphological stability of δ-ferrite/γ interphase boundary has been established. Thereafter, the criterion expression for morphological stability of δ-ferrite/γ interphase boundary was established and discussed, and the critical migration speeds of δ-ferrite/γ interphase boundaries are calculated in Fe-C, Fe-Ni, and Fe-Cr alloys. The results indicate that the δ-ferrite/γ interphase boundary is very stable and nearly remains absolute planar all the time during γ → δ transformation in Fe-C alloy. The δ-ferrite/γ interphase boundary remains basically planar during δ → γ transformation when the migration speed is lower than 0.88 μm/s, and the interphase boundary will be unstable and exhibit a finger-like morphology when the migration speed is higher than 0.88 μm/s. The morphological stability of δ-ferrite/γ interphase boundary is primarily controlled by the interface energy and the solute concentration gradient at the front of the boundary. During the constant temperature phase transformation, an opposite temperature gradient on both sides of δ-ferrite/γ interphase boundary weakens the steady effect of the temperature gradient on the boundary. The theoretical analysis of the morphological stability of the δ-ferrite/γ interphase boundary is coincident with the observed experimental results utilizing the HTCSLM. There is a good agreement between the theoretical calculation of the critical moving velocities of δ-ferrite/γ interphase boundaries and the experimental results. 相似文献
5.
The in-situ continuous cooling β-to-α transformation kinetics of extra-pure (EP) Ti and of grade-4 commercially pure (CP) Ti were investigated using a fully computer-controlled
resistivity-temperature realtime measurement apparatus and transmission electron microscopy. The β-to-α′ martensitic transformation occurs under near pure shear condition, and the habit plane of lath-type martensite was determined
to be
parallel to
, which is in good agreement with the prediction of the crystallographic theory. The M
s
temperature of EP-Ti was measured as 800 °C and can be raised by up to about 40 °C due to the generation of thermal stress
and local deformation during rapid cooling. The massive transformation was, for the first time, observed to occur over a wide
range of cooling rates in an EP-Ti. The massive start temperature and its occurrence were, unlike the martensitic transformation,
hardly affected by the generation of thermal stress and local deformation during rapid cooling. The stable regime of massive
transformation in a grade-4 CP-Ti was considerably shifted toward a slower cooling rate side and was significantly contracted
at the same time. This is because the presence of iron impurity not only largely suppresses the massive transformation but
also significantly delays a long-range diffusional transformation. 相似文献
6.
Small angle neutron scattering (SANS) has been used to evaluate the temporal evolution of the secondary and tertiary γ′ precipitates in the nickel-base superalloy, RR1000, in situ during an aging heat treatment at 1033 K (760 °C) following a supersolvus heat treatment and oil quench. The bimodal distribution of secondary and tertiary γ′ was analyzed using a specially developed polydispersive model capable of evaluating the scattering curves to obtain precipitate size distributions (PSDs) and volume fractions as a function of time. The model was designed to be suitable for high volume fractions of γ′ and takes into account the scattering interaction between precipitates. The results show an increase in the volume fraction and the mean particle size of both the secondary γ′ and tertiary γ′ during aging. The initial and final precipitate distributions have been characterized using transmission electron microscopy (TEM) and show satisfactory correlation with the SANS data across the scattering vector range. 相似文献
7.
Yongmei M. Jin Armen G. Khachaturyan Yu U. Wang Chris R. Krenn Adam J. Schwartz 《Metallurgical and Materials Transactions A》2005,36(8):2031-2047
A new stress-accommodating crystallographic mechanism of the δ→α martensitic transformation in plutonium alloys is proposed. According to this mechanism, an orientation variant of the α phase is produced by a combination of a homogeneous strain and shuffling of the alternating close-packed (111)
δ
planes. It is shown that the formation of stable transformation-induced twins whose twin-plane orientations and twin-shear
directions do not depend on the small variations of the crystal-lattice parameters is the preferred stress-accommodating mode.
Only these stable twins have dislocation-free twin boundaries, while the twin boundaries of all others are decorated by an
ultradense distribution of partial dislocations. The theory predicts a crystal-lattice rearrangement mechanism involving the
(205)
α
stable twins. The corresponding invariant plane-strain (IPS) solutions, with special emphasis on the two simplest shuffling
modes (the single and double elementary modes), are presented and compared with the existing experimental observations. It
is shown that the habit-plane orientation is highly sensitive to the input values of the crystal-lattice parameters and, especially,
to the accuracy of the measured volume change in the δ→α transformation. An analysis of these effects on the habit-plane orientation and orientation relations is also presented. 相似文献
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D.J. Sordelet R.T. Ott M.Z. Li S.Y. Wang C.Z. Wang M.F. Besser A.C.Y. Liu M.J. Kramer 《Metallurgical and Materials Transactions A》2008,39(8):1908-1916
The structure of hyper-eutectic Zr
x
Pt100−x
(73 ≤ x ≤ 77) metallic glasses produced by melt spinning was examined with high-energy synchrotron X-ray diffraction (HEXRD) and
fluctuation electron microscopy. In addition, details of the amorphous structure were studied by combining ab initio molecular dynamics and reverse Monte Carlo simulations. Crystallization pathways in these glasses have been reported to vary
dramatically with small changes in compositions; however, in the current study, the structures of the different glasses were
also observed to vary with composition, particularly the prepeak in the total structure factor that occurs at a Q value of around 17 nm−1. Results from simulations and fluctuation electron microscopy suggest that the medium-range order of the amorphous structure
is characterized by extended groups of Pt-centered clusters that increase in frequency, structural order, or spatial organization
at higher Pt contents. These clusters may be related to the Zr5Pt3 structure, which contains Pt-centered clusters coordinated by 9Zr and 2Pt atoms.
This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February
25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of
Materials Committee.
相似文献
D.J. Sordelet (Senior Scientist and Group Leader)Email: |
11.
R. W. L. Fong R. Miller H. J. Saari S. C. Vogel 《Metallurgical and Materials Transactions A》2012,43(3):806-821
The phase transformations in an as-received Zr-2.5Nb pressure tube material were characterized in detail by neutron diffraction.
The texture and volume fraction of α and β phases were measured on heating at eight different temperatures 373 K to 1323 K (100 °C to 1050 °C) traversing across the
α/(α + β) and (α + β)/β solvus lines, and also upon cooling at 1173 K and 823 K (900 °C and 550 °C). The results indicate that the α-phase texture is quite stable, with little change in the {0002} and { 11[`2]0 } \left\{ {11\bar{2}0} \right\} pole figures during heating to 1123 K (850 °C). The β-phase volume fraction increased while a slight change in texture was observed until heating reached 973 K (700 °C). On further
heating to 1173 K (900 °C), there appears a previously unobserved α-phase texture component due to coarsening of the prior primary α grains; meanwhile the transformed β-phase texture evolved markedly. At 1323 K (1050 °C), the α phase disappeared with only 100 pct β phase remaining but with a different texture than that observed at lower temperatures. On cooling from the full β-phase regime, a different cooldown transformed α-phase texture was observed, with no resemblance of the original texture observed at 373 K (100 °C). The transformed α-phase texture shows that the {0002} plane normals are within the radial-longitudinal plane of the pressure tube following
the Burgers orientation relationship of (110)bcc//(0002)hcp and
[[`1]11]\textbcc //[11[`2]0]\texthcp [\bar{1}11]_{\text{bcc}} //[11\bar{2}0]_{\text{hcp}} with a memory of the precursor texture of the primary α grains observed on heating at 1173 K (900 °C). 相似文献
12.
The elastic properties of Ni x W1?x alloys up to x = 0.1875 have been determined from first principles calculations. We have used stress–strain relationships to calculate the C ij elastic coefficients and the Voigt–Reuss–Hill approximations to determine the bulk and shear moduli of polycrystals. The W alloying increases the compression modulus while the shear modulus remains almost constant. Furthermore, the W alloying has a minor effect on the elastic anisotropy and, therefore, on its contribution to the indentation modulus. 相似文献
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Yu. V. Verbovytskyy V. V. Shtender P. Ya. Lyutyi I. Yu. Zavaliy 《Powder Metallurgy and Metal Ceramics》2017,55(9-10):559-566
14.
Kwai S. Chan 《Metallurgical and Materials Transactions A》2004,35(11):3409-3422
The yielding behavior of individual Widmanstätten α (hcp) + β (bcc) colonies of Ti-8Al-1Mo-1V has been analyzed theoretically by considering the shearing of β platelets by slip in the α phase. Slip is assumed to initiate in the softer α phase and impinges on the harder β platelets. Under the combined actions of the external stress and impinging slip, yielding of the β platelets occurs when the von Mises effective stress in the β phase exceeds a critical value. The theoretical analysis indicates that the macroscopic slip planes in individual Widmanstätten colonies correspond to those that induce the highest stresses in the β platelets. In addition, the yield stress and the strain-hardening rate both increase with decreasing values of the angle, β b , between the slip direction and the normal to the β platelets, resulting in soft and hard slip orientations. Soft orientation of the lamellar colony is associated with α slip parallel to the macroscopic, serrated α/β interface, which includes crystallographic interface and ledges, while the hard orientation is associated with slip normal to the thin platelets. This slip anisotropy appears to arise from increasing difficulty of slip transmission across the macroscopic α/β interface when the operative slip vector impinges perpendicular to the β platelets. 相似文献
15.
The effect of the Li ion concentration on the phase composition, the electrical conductivity, and the thermoelectric power of the LaLi y Co1–yO3–δ (0 ≤ y ≤ 0.1) oxides synthesized by cocrystallization has been studied. It is found that the region of the perovskite-like solid solution LaLi y Co1–yO3–δ is no higher than y = 0.037. In the temperature range 300–1020 K, lithium alloying leads to an increase in the electrical conductivity and a decrease in the positive thermoelectric power of the single-phase samples compared to LaCoO3–δ. The results are discussed using the density of states model proposed by Senarus Rodriguez and Goodenough for LaCoO3–δ and La1–xSr x CoO3–δ and using the Mott theory of noncrystalline substances. 相似文献
16.
The relationship between heat-treatment parameters and microstructure in titanium alloys has so far been mainly studied empirically,
using characterization techniques such as microscopy. Calculation and modeling of the kinetics of phase transformation have
not yet been widely used for these alloys. Differential scanning calorimetry (DSC) has been widely used for the study of a
variety of phase transformations. There has been much work done on the calculation and modeling of the kinetics of phase transformations
for different systems based on the results from DSC study. In the present work, the kinetics of the β ⇒ α transformation in a Ti-6Al-4V titanium alloy were studied using DSC, at continuous cooling conditions with constant cooling
rates of 5 °C, 10 °C, 20 °C, 30 °C, 40 °C, and 50 °C/min. The results from calorimetry were then used to trace and model the
transformation kinetics in continuous cooling conditions. Based on suitably interpreted DSC results, continuous cooling-transformation
(CCT) diagrams were calculated with lines of isotransformed fraction. The kinetics of transformation were modeled using the
Johnson-Mehl-Avrami (JMA) theory and by applying the “concept of additivity.” The JMA kinetic parameters were derived. Good
agreement between the calculated and experimental transformed fractions is demonstrated. Using the derived kinetic parameters,
the β ⇒ α transformation in a Ti-6Al-4V alloy can be described for any cooling path and condition. An interpretation of the results
from the point of view of activation energy for nucleation is also presented. 相似文献
17.
John W. Foltz Brian Welk Peter C. Collins Hamish L. Fraser James C. Williams 《Metallurgical and Materials Transactions A》2011,42(3):645-650
Beta-Ti alloys contain sufficient concentrations of β stabilizing alloy additions to permit retention of the metastable β phase after cooling to room temperature. Decomposition of the metastable β phase results in the formation of several possible phases, at least two of which are metastable. Concurrently, equilibrium
α phase often forms first by heterogeneous nucleation at the α grain boundaries with an accompanying precipitate free zone observed adjacent to the grain boundary α. The grain boundary regions are softer than the precipitation hardened matrix. As a consequence, fracture follows the prior
β grain boundaries, especially in high-strength conditions. This fracture mode results in low tensile ductility and/or fracture
toughness. This article will describe methods of minimizing or eliminating grain boundary α formation by using metastable transition precipitates to nucleate α more rapidly. The effects on fracture behavior also will be described. 相似文献
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Yuanbiao Tan Wenchang Liu Song Xiang Fei Zhao Yilong Liang 《Metallurgical and Materials Transactions A》2018,49(12):6040-6045
The effect of β grain size on stress-induced martensitic transformation in β solution-treated 51.1Zr-40.2Ti-4.5Al-4.2V alloy was investigated by using XRD and TEM techniques. The results show that initial β grain size has a profound effect on the triggering stress of the stress-induced martensitic (SIM) transformation. The triggering stress increases with increasing initial β grain size. The SIM transformation significantly affects the deformation behavior of the alloy. A typical double yielding is observed in the stress-strain curves due to the occurrence of the SIM transformation. The curve of work hardening rate vs. true strain is divided into three stages for the samples with small β grain size. The work hardening rate at stage ΙΙ or ΙΙΙ decreases with increasing initial β grain size, which is attributed to the effect of the SIM transformation during a tensile test. 相似文献